Catalytic fast pyrolysis of waste pepper stems over HZSM-5

• Fast pyrolysis of waste pepper stem was conducted over HZSM-5 with different acidity.
• Catalytic pyrolysis reduced phenolics and acids, while increasing hydrocarbons.
• HZSM-5 with a higher acidity showed a higher catalytic activity.
• Conversion of carbohydrate via furans to aromatics over strong acid sites was observed.
• Catalytic pyrolysis of lignin-rich biomass can be used to produce valuable chemicals.

Catalytic fast pyrolysis over HZSM-5 of red pepper stems, a representative agricultural residue material in the southern area of South Korea, was carried out. The SiO2/Al2O3 ratio of the catalyst were 23 and 280. Pyrolysis-gas chromatography/mass spectrometry was used to pyrolyze the pepper stem samples at 550 °C and directly analyze the product distribution. The main product species of the non-catalytic pyrolysis of pepper stems were phenolics, followed by oxygenates and acids. The production of aliphatic and aromatic hydrocarbons was marginal. On the contrary, catalytic pyrolysis over HZSM-5 reduced the fractions of phenolics and acids significantly, while considerably increasing the fractions of aliphatic and aromatic hydrocarbons. The catalytic activity of the HZSM-5 with a SiO2/Al2O3 ratio of 23 was much higher, owing to its much larger amount of strong Brønsted acid sites, than the one with a SiO2/Al2O3 ratio of 280. Conversion of carbohydrate via furans to aromatics over strong acid sites was observed, which was in good agreement with previous studies. This study suggests that the catalytic pyrolysis of lignin-rich biomass over acidic zeolite catalysts can be a promising method to produce valuable chemicals such as aromatic compounds.